Mercury 700 two stroke question

[telebrewer77]

Hi all,
this is my first post here in the forum. I have a 1978 mercury 700, 70 hp, 2 stroke outboard. I can get it to run like an angry weed eater with earmuffs on in my driveway but as soon as we get it in the water it runs very weakly and sputters out when I engage the clutch in the water. Weirdest thing. It is at a flatter angle in my driveway, but I can't figure out why it runs like a top on land and like a sick chainsaw on the water. Needless to say, I've adjusted the carbs and cleaned the heck out of them, but still can't figure it out. Any help from anybody with a little 70s mercury 2 stroke knowledge would be appreciated!

 

[jhow0228]

Re: Mercury 700 two stroke question

Have you cleaned/checked the exhaust out?

 

[telebrewer77]

Re: Mercury 700 two stroke question

No, I haven't really checked it out very much. Do you think it might be like a back pressure problem?

 

[jhow0228]

Re: Mercury 700 two stroke question

It could be. If the exhaust is through the hub and the hub isn't submerged and it runs fine, then once its submerged it spits, sputters, and dies. It may very well be that.

 

[telebrewer77]

Re: Mercury 700 two stroke question

That makes total sense, I never thought of that. I guess if its getting too much back pressure would explain why it only happens in the water. Thanks I'll give it a try and report back!

 

[oldman570]

Re: Mercury 700 two stroke question

The final carb/timming setting has to be done on the water or in a test tank for everything to be correct. The backpressure on the exhaust dose make a big difference. You should never run the motor on muffs more than a high idle as damage to the motor can happen from over revving. JMO
Oldman570

 

[telebrewer77]

Re: Mercury 700 two stroke question

Thank you gentlemen. After taking off the bottom end off and pulling it out, we heard what we thought was a parts falling into our test tank, and low and behold we found 2 large caked on chunks of nasty exhaust buildup. We cleaned it out rest of the exhaust really well, and got her back in the tank and wow what a difference. Not only does it run strong, it doesn't bog down when I put it into gear, it runs like a champ. I'm looking forward to getting her on the lake this week to finally see it really run like it should. Thanks for the knowledge gentlemen!